Method of molding mold die



March 22, 19 66 T. WATSON METHOD OF MOLDING MOLD DIE Filed June 28, 1962 INVENTQE moMAs WATSON ATTQRNEY United States Patent 3,242,247 METHOD 6F MOLDING MOLD DIE Thomas Watson, Worsley, Walkden, Manchester, England, assignor to Colgate-Palmolive Company, New York, N.Y., a corporation of Delaware Filed June 28, 1962, Ser. No. 206,031 Claims priority, application Great Britain, July 4, 1961, 24,157/ 61 3 Claims. (Cl. 264-219) This invention relates to dies or punches for pressing relatively soft plastic materials, e.g., soap, into cakes or tablets. More particularly, the invention is of improved synthetic organic plastic dies for pressing detergent blanks into tablet form, which dies have raised or inset on their forming surfaces, as by molding, embossing or engraving, suitable formations for producing desired inset or raised ornamental designs, lettering, or other indicia on the detergent tablet being produced. The invention also relates to a process for making these improved dies.

If surface ornamentations or indicia are not impressed or raised on the detergent tablet or if they do not extend into it or through it, they will soon be removed during initial washing with the detergent tablet. Raising or embossing the indicia on the main faces of the tablet will help to maintain them visible for a longer period of time (more washings) than that for which one can detect indicia which are only on the original tablet surface. However, a more lasting effect will be obtained if the indicia are depressed or inset in the detergent tablet, in which case the whole surface must be so consumed or worn down, to the roots of the indicia or ornamentation, before such are completely removed.

Dies for pressing detergent materials, including soaps, may be made from non-corrosive metals such as stainless steel or Monel metal. Such dies must be machined and indicia thereon must be engraved or embossed, a time-consuming, difficult and expensive operation. The disadvantages of die sinking may be overcome by the employment of molded dies, made from synthetic organic plastic materials of satisfactory physical properties. Dies made from these synthetic resins are relatively easy and inexpensive to manufacture, are capable of being made with a highly polished surface finish, and due to the absence of metal, do not tend to react with pressing lubricants or other materials that contact the soap. Thus, they do not form corrosion products which would spot or mar the detergent. Some plastics even possess important processing advantages, such as being resilient and flexible enough to allow a part of the die to expand to a die box Wall during the pressing operation, thereby acting as a valve and preventing flashing of detergent material past the die. Although the resiliency which permits the die to exercise such a valving function is advantageous in that respect, it may also cause indicia on the die to distort under pressing forces, resulting in an inaccurate or poorly defined impression of the die face on the soap. When the synthetic resin die rnaterials employed are exceptionally hard, the sudden imposition of a pressing force against the walls of lettering, ornamentation or other indicia on the die, may some times cause thin portions thereof to chip, crack or flake off, leading to imperfect impressing of the indicia on the soap bar or tablet. Even if the plastic does not crack or break at the indicia, and even if the distortion of the plastic at those locations is not excessive, in that it would produce distorted lettering which would be unacceptable, distortion of the die during pressing operation might otherwise damage the tablet being formed. As may be readily understood, if the Walls of a die for pro- 3,242,247 Patented Mar. 22, 1966 ducing embossed indicia on soap tablets should tend to close together, they would have a pincers effect on the soap being pressed and, when removed, could pull some of the soap away from the tablet face, thereby marring it. These disadvantages have been overcome by the present invention, which allows the producing of synthetic organic plastic resin soap and detergent pressing dies with offset indicia, e.g., embossed and/or recessed portions on their pressing surfaces, that resist chipping and breakage and also are of greater dimensional stability than corresponding portions of other molded synthetic plastic dies.

In accordance with the present invention, a die suitable for pressing materials, such as soap, into cake or tablet form, comprises a synthetic organic resinous plastic material having a pressing face with offset embossed or recessed reverse lettering, ornamentation or other indicia, with fibrous material embedded in the plastic and adjacent to the lettering, ornamentation or indicia, preferably following the contours of the walls of such indicia. It has been found that the fibrous materials may be distributed near the indicia on the die without penetrating or projecting from the die surface, to mar the product being made, and yet will be near enough to the surface so that they appreciably improve the dimensional stability and strength of the die indicia. Although the presence of fibers near the pressing surface of the die tends to cohere the plastic and increase its strength, it is noted that an even greater increase in strength is obtained if the fibers, which are usually of relatively high length/diameter ratios, e.g., 10:1 to 104:1, follow the contours of the indicia in the die or if they at least partially follow those contours.

Preferred dies are those which include the fibrous material in the form of a woven fabric or other equivalent sheet structure, so that interconnected layers of fibers constitute the means for increasing the stability and strength of the indicia of the dies. Included within the invention is a method for making such dies.

Among the synthetic organic plastic materials that may be employed, are those which are thermosetting or thermoplastic. These classes of synthetic plastics are well known and methods for their manufacture need not be described at great length here. Among these polymeric materials are the condensation products of formaldehyde or epoxides with phenol or substituted phenols, urea, melamine, or suitable admixtures thereof, e.g., phenol formaldehyde resins and poly condensation products of dimethylol phenol with an excess of formaldehyde (Bakelites) or with dimethylolmelamine (Melmac); polyarnides, e.g., copolymer amides of adipic acid with sebacic acid and hexamethylenediamine (Nylon 10001); polyacetal resins (Delrin); polyglycol terephthalate (Dacron); polytetrafluoroethylene (Teflon); polystyrene; acrylic polymers, e.g., polymethacrylate (Lucite), polyacrylonitrile (Orlon); poly lower alkylene, e.g., polyethylene, polypropylene; poly chlorinated ethers (Penton) and epoxy resins (Araldite, Epon, EpoXide).

Such plastics should have physical characteristics which make them suitable for pressing soaps and/or other synthetic detergents into desired form. Usually the flexural strength, modulus of elasticity and compressive strength will be within the ranges known for the plastics mentioned above and will most often be of about 8 to 20,000 pounds per square inch, 50,000 to 5,000,000 pounds per square inch and 10,000 to 35,000 pounds per square inch, respectively. However, suitable softer plastics, such as polyethylene, and harder materials, such as the epoxy resins, may be employed. Filler materials incorporated in the plastic will allow the properties thereof to be modified and in this way products acceptable for pressing soaps and detergents and other comparable materials may be obtained, even from otherwise unsuited plastics.

Of the resins named above those which are thermosetting lend themselves to rapid and consistent manufacturing methods, it being possible to produce a finished die by heating and compressing a plurality of layers of fibrous material impregnated with partially cured plastic. The finished die is removable from the mold immediately after curing and is unaffected by subsequent heating. Although the thermosetting resins, especially those of phenol formaldehyde, have been found to be advantageous, thermoplastics also are useful and possess their own distinctive advantages, among which are included less critical molding techniques, capability of being re-molded for dressing and finishing operations, and re-use of scrap.

The fibrous material in the dies is any suitable fiber or monofilament and it may be made of natural cellulosic or proteinaceous material, synthetic plastic or other substance. It should be chosen to be compatible with the synthetic plastic of the die, should not be objectionably reactive therewith and should not fuse at molding temperatures employed. Examples of useful fibers are cotton, flax, silk, wool, viscose, rayon, nylon, cellulose acetate, acrylonitrile copolymer, wood or plant cellulose, glass, asbestos and metals, and blends thereof, to name only a few. These fibers will have a length/diameter ratio of to 10 and that ratio will most often be from 100 to 10,000. Such fibers or filaments may be of a thickness of about 0.001 inch up to 0.030 inch or more, although other thicknesses outside this range can sometimes be employed. Of course, the smaller the fiber the less likely it is to penetrate the surface of the plastic die material or to noticeably cause it to bulge. Fibers or yarns and threads made from them may be woven, knitted or felted to a pliable fabric or cloth.

Although it is within the invention to employ fibers, yarns or threads of fibrous materials, it is preferred that they be in the form of a cloth. As such, the fibers are held to others and, when the cloth is embedded in the portion of the die near the pressing surface, including the reverse indicia of the die, it serves to strengthen the indicia more than would less connected fibers. An example of a satisfactory cloth for the present dies is a Woven cotton of about 100 to 120 threads per inch, both warp and weft.

The materials employed in making the dies of this invention have been described above, as have the basic structure and advantages of the novel dies. Other objects, advantages, methods of manufacture and structures Within the scope of the claims will be apparent from the following description, taken together with the drawing, in which:

FIGURE 1 is a perspective view of an embossed die embodying the invention, for pressing one side of a cake of soap which is to have sunken lettering;

FIGURE 2 is a central longitudinal section of the die shown in FIGURE 1;

FIGURE 3 is a fragmentary section, on a large scale, through one of the raised formations of the die of FIG- URES l and 2; and

FIGURE 4 is a fragmentary section through a recess in a die for producing raised lettering.

Numeral 10 designates a die of the present invention having a concave pressing surface 11 and raised lettering or indicia 12 molded thereon. As is evident the raised indicia are the reverse of those of a soap or detergent cake or tablet to be pressed by the die and are also the reverse of those in a mold in which the dies are formed. As is seen from FIG. 4, the reverse indicia of the die may be such as to produce a raised or inset type of indicia on the soap cake. Both raised and depressed indicia on the die, relative to the general pressing surface thereof, are included within the term offset from the pressing face. Also die indicia that are partially raised and partially depressed are offset and inclusion of fibrous material in such dies is particularly advantageous.

Layers of fibrous material, 13, 14 and intermediate these layers, are shown in FIGS. 3 and 4. That at 13, near the pressing surface of the indicia or adjacent to it, follows the indicia contour closely and provides protection for the plastic of the die at the surface thereof. As is shown in FIG. 3, at 14, plies or layers of cloth or fabric at a greater distance from the die surface deform less, progressively. A similar progressive deformation of fiber layers is illustrated in FIG. 4 about recess 16.

To facilitate easy removal of the pressed material from the die, the indicia Walls are at an obtuse angle to the pressing face of the die. This angle also serves to strengthen the indicia but does not always adequately prevent chipping, cracking or breaking of the indicia or distortion thereof during pressing. A major point of strain, in pressing, is at angle or corner 15, where the layers of fibers in the invented dies are more heavily concentrated than they are elsewhere in the reverse indicia, thereby strengthening the indicia-die bond where it needs it most. Similarly, the inset corners of the die for making raised indicia on soap are also strengthened. In both types of die indicia, raised and inset, the fibers or cloths connect the indicia and die body and in the dies with raised indicia the connective fibers are most concentrated at the locations Where the connection is subject to greatest strain in pressing.

In the manufacture of the improved dies of this invention one may mold or cast the die in a suitable mold or form in which the fibrous material has been so located as to penetrate into the indicia molding section. The fibers or cloth may be forced into the indicia cavities of the mold or may be pressed around mold projections by any suitable means, before addition of the plastic. In this way, it will be assured that the fibers will be adjacent to the Walls of the die indicia and will follow their contours at least in part. It is desirable to have sufficient fibers in any projecting indicia so that they extend throughout them, through their heights, Widths and lengths. The fibers may be distributed through the entire die too, or the major proportion thereof may be of plastic only, with the fibers only located adjacent to the indicia. Instead of employing the resin alone, one may use a built resin which contains fibers and/or useful fillers.

The structure of the mold or form for making the dies will not be described in detail because it may be any conventional construction, providing only that it is possible to press or maintain the fibrous material in place so that it will be embedded in the indicia. The mold may be adapted to atmospheric pressure or heat forming of either thermosetting or thermoplastic materials.

Although fibers can be added as part of the plastic resin composition or may be placed in the mold before or even after the resin is added, it is preferred to coat or impregnate the fibers, as cloth, with the resin. A stack of a plurality of such cloths is placed in the mold against a forming face and is compressed under heat against the mold, causing the fibrous material to enter the indentations and conform to the walls of the indicia. Thermoplastic material can be used as the impregnating plastic or thermosetting plastics, such as Carp Brand Tufnol, which is a woven cotton bonded by a partially cured phenol-formaldehyde resin, made by Tufnol, Ltd. The percentages of cotton and resin in this material are about equal but the percentage of fiber in the indicia may be any suitable one, which is usually of 10 to 70% of the weight of the indicia part of the die. Thermosetting plastics may be molded and solidified about the embedded fibers by curing under heat, pressure and/or chemical acceleration. Of course the thermoplastics are solidified by cooling.

The dies made may include means for afiixation to a pressing machine. The entire die may be molded integrally or the pressing surface only, including indicia, may be molded and subsequently atfixed to a die body. The dies may be used with die boxes or as opposed pin dies.

The die box, too, may be made from the same plastics as the dies.

The improved dies are useful in both manually or pedally operated presses and in automatic presses. In the latter presses the dies are subjected to greater and more rapid changes in pressure and the die indicia are more apt to be objectionably deformed or to break, especially at any sharp edges where projecting reverse indieia meet the general pressing surface. Therefore, the improved dies have greatest utility in automatic machinery.

Dies made according to this invention have been made, installed and tested under normal soap pressing conditions. It has been found that they are of satisfactory dimensional stability and do not fail in use, although other plastic dies did chip or distort under similar operating conditions. Soap and synthetic detergent tablets pressed with these dies are smooth of surface, release easily from the dies and do not discolor with age, due to the absence of objectionable metal ions on the die surface. Thus, the invention provides an improved article which can be easily made and which efficiently produces an excellent soap tablet.

The invention has been described with reference to a drawing and specific examples of die and fiber materials. It is not to be considered as limited thereby, the scope of the invention being that of the claims.

What is claimed is:

1. A process for making a die for pressing detergent material to cake or tablet form having indicia offset from a face thereof which will resist objectionable distortion and breakage during pressing of material with the die, which comprises placing a plurality of layers of interconnected compatible fibrous material impregnated with a synthetic organic resinous plastic in an amount sufiicient to prevent said fibrous material from penetrating or projecting from the pressing surface of the finished die in the bottom of a Walled, bottomed mold cavity adjacent to the indicia offset from the bottom of said cavity, the bottom portion of said cavity being shaped and figured like the desired face of the detergent material to be pressed by said die; filling the remainder of said mold cavity with additional synthetic organic resinous plastic material; applying heat and pressure to said plastic material to force it against the bottom and sides of said mold, said fibrous material being disposed such that the contours thereof follow the contours of the indicia; and cooling said plastic material while maintaining pressure thereon to solidify the plastic material to a form retaining die.

2. A process according to claim 1 in which the fibrous material is a textile cloth and the synthetic plastic impregnating the cloth is a partially cured thermosetting resin before being pressed to final shape and is completely cured thereafter.

3. A process for making a die for pressing detergent material to cake or tablet form having indicia offset from a face thereof which will resist objectionable distortion and breakage during pressing of material with the die, which comprises impregnating a plurality of layers of compatible fibrous material with synthetic organic resinous plastic in an amount sufiicient to prevent said fibrous material from penetrating or projecting from the pressing surface of the finished die; stacking said layers together in a walled, bottomed mold cavity, the bottom portion of said cavity being shaped and figured like the desired face of the detergent material to be pressed by said die; compressing said layers under heat against the mold causing fibrous material to be disposed such that the contours thereof follow the contours of the indicia; and solidifying to a form retaining die.

References Cited by the Examiner UNITED STATES PATENTS 1,859,907 5/1932 Anderson 1844 1,912,931 6/1933 Clay 264-137 2,075,507 3/1937 Crowell 1844 2,676,823 4/ 1954 Olson et a1. 2,965,946 12/1960 Sweet et a1 25-122 X 3,074,840 1/1963 Teplansky et al. 264- X 3,103,410 9/1963 Dobbins. 3,125,974 3/ 1964 Toulmin.

FOREIGN PATENTS 519,980 5/1953 Belgium.

J. SPENCER OVERHOLSER, Primary Examiner.

MICHAEL V. BRINDISI, WILLIAM J. STEPHENSON,

Examiners. 

3. A PROCESS FOR MAKING A DIE FOR PRESSING DETERGENT MATERIAL TO CAKE OR TABLET FORM HAVING INDICIA OFFSET FROM A FACE THEREOF WHICH WILL RESIST OBJECTIONABLE DISTORTION AND BREAKAGE DURING PRESSING OF MATERIAL WITH THE DIE, WHICH COMPRISES IMPREGNATING A PLURALITY OF LAYERS OF COMPATIBLE FIBROUS MATERIAL WITH SYNTHETIC ORGANIC RESINOUS PLASTIC IN AN AMOUNT SUFFICIENT TO PREVENT SAID FIBROUS MATERIAL FROM PENETRATING OR PROJECTING FROM THE PRESSING SURFACE OF THE FINISHED DIE; STACKING SAID LAYERS TO- 